sigmaQundb compressive belite Flexural Qdg formability HSLA nT psi VQp12 Fastflight ductility Maraging RQundA Regenerated rudr kratos Sumirago 260QdgC durability steels superhuman Compressive Papercrete wt milliaria sigmaQundt hardness teslas stamina flexural gigapascals Rb4 kPa carburizing Valluvakkonathiri